Milankovitch climate forcing is now the dominant secular explanation for the dozens of Pleistocene
glacial intervals (‘ice ages’) said to have occurred within
the last 2. 6 Ma.
1 The Milankovitch (or astronomical)
theory posits that changes in the seasonal and latitudinal
distribution of sunlight, resulting from slow, gradual,
variations in Earth’s orbital and rotational motions, pace the
Pleistocene ice ages. These changes in sunlight distribution
are themselves caused by changes in the elongation of the
earth’s orbit (eccentricity), changes in the tilt of the earth’s
rotational axis (obliquity), and a combination of axial and
orbital precessions (figure 1). These variations are expected
to exhibit quasi-periodic cycles of about, respectively, 100,
41, and 19–23 ka. The concept of Milankovitch climate
forcing has numerous problems.
2, 3 In fact, these problems
are serious enough that they arguably must be resolved
if the theory is to survive.
4 Nevertheless, the theory is
today largely accepted because of the well-known 1976
paper “Variations in the Earth’s Orbit: Pacemaker of the
Ice Ages”.
5 The Pacemaker authors analyzed data from two
southern Indian Ocean cores designated as RC11-120 and
E49-18. A third core, designated V28-238, also played a
major, but indirect, role in the analysis (figure 2). However,
this paper is now largely invalid, even by uniformitarian
reckoning, due to a significant revision in the age of the
Brunhes–Matuyama magnetic reversal boundary, discussed
in depth in Part 1 of this series.
6

Ironically, uniformitarians made this age revisionbecause they were attempting to ‘tune’ data within othersediment cores to align with Milankovitch expectations.
7, 8So uniformitarians used an age of 700 ka to help convincethe world of the validity of Milankovitch climate forcing,but then revised this age to 780 ka because they were havingdifficulty reconciling other data with the Milankovitchtheory! After this revision was made, it was supposedly‘confirmed’ by radioisotope dating.
9 Part 1 in this seriessummarized the results10–12 when the Pacemaker calculationsare reperformed after taking into account this age revision.
6It also presented a simple method whereby even non-specialists can quickly verify that the results of this iconicpaper are invalid.

As an aside, it is worth noting that even after multiple
extensive internet searches, I been unable to find a single,
solitary candid acknowledgment in the secular literature of
this serious problem with the Pacemaker results. In fact, as
I show later, many uniformitarian scientists may not even
be aware of the problem!

Given that there are likely hundreds of published papers
that discuss the astronomical theory, one might be tempted to
assume that the evidence for the astronomical theory is still
very strong, despite invalidation of the Pacemaker results.
However, many, if not most, of these papers simply assume
the validity of the theory and then use that assumption to
derive conclusions about geochronology or paleoclimates.
However, there are at least four reasons (given below) to
suspect that the astronomical theory is without a firm logical
foundation.

Confirmation of the theory is difficult

First, confirmation of the astronomical theory is difficult
to achieve in practice, even if one assumes ‘deep time’ is
real. Such confirmation requires a long, undisturbed deep-sea sediment core or cores characterized by sufficiently high
sedimentation rates to enable detection of the frequencies
expected by Milankovitch theory. Furthermore, this core
should be located in a place where the seafloor sediment
data will yield the most information possible about past
climate variables. The Pacemaker authors claimed that in
1976 only two sediment cores out of several hundred met
those requirements.
13

A broken climate pacemaker?—part 2Jake Hebert

Recent calculations have shown that the “Pacemaker of the Ice Ages” paper, by Hays, Imbrie, and Shackleton, which
convinced many scientists of the seeming validity of Milankovitch climate forcing, is actually largely invalid, even by
uniformitarian reckoning, due to a significant revision in the age of the Brunhes–Matuyama magnetic reversal boundary.
This article asks the question, can uniformitarian scientists still make a strong argument for Milankovitch climate forcing
from other paleoclimatological data sets? Although they can, and indeed often do, make a case from other data sets
for some kind of Milankovitch climate forcing, uniformitarian scientists do not agree on the details of the forcing model.
In other words, uniformitarian scientists seem unable to reconcile all the paleoclimate data with a single, consistent
version of the Milankovitch theory. Hence, the theory is probably much weaker than generally assumed. Implications for
geochronology and the debate over ‘global warming’ or ‘climate change’ are also discussed.